Suppression of the total secondary electron yield (TEY) of metal surfaces is important in many areas such as accelerator, satellite, and Hall thruster. Among TEY suppression techniques, micro-porous surfaces have been demonstrated as an effective method. In this work, we developed an analytical model that is able to obtain the contributions of TEY from both the 1st and 2nd generation secondary electrons (SEs). Calculation results show that the TEY contributed by the bottom of the hole dominates the TEY of the micro-porous surface with the aspect ratio we have chosen. Thus, we developed the following design guidance for the improvement of the TEY suppression efficiency of the micro-porous surface: either lower the TEY of the bottom or guide its SEs to the lateral side of the hole. To verify this idea, we performed the following numerical simulations: a micro-hole with its inner surfaces coated with a low TEY material and a micro-hole with nano-triangular grooves or nano-truncated cone pillars embedded at its bottom. Compared with a usual micro-hole, the proposed hybrid micro/nano structures show improved TEY suppression efficiency as expected from the analytical model. The percentage ratios of the 1st and 2nd generation SEs obtained from the simulation agree well with the predictions of the analytical model. What is more, we also present the results of the emitting angle distribution of SEs which represent remarkable deviation from the usual cosine distribution.

Multipactor induced by secondary electron emission (SEE) is a potential risk for many high-power systems. It is of great importance to suppress the total electron emission yield (TEEY) to mitigate the detrimental effect. Metal black has been reported as effective TEEY suppressor, but the theoretical model for describing its SEE characteristics is still scarce. In this work, we propose a periodic nanostructure model, with each unit composed of a combination of a top hemispherical nanograin and a fractal rectangular groove-like gap, to describe the silver black nanostructure. Using this model, we investigate the SEE characteristics of the silver black nanostructure theoretically. Simulation results indicate that the groove-like gaps in the nanostructure suppress the TEEY, while the top hemispherical nanograins enhance it; and the suppression on the true secondary electron yield is much stronger than that on the back-scattered electron yield (BSEY). In addition, we observe two interesting phenomena: first, the nanostructure enhances the BSEY even if it suppresses the TEEY when the proportion of top nanograins reaches 30%; second, the suppression on TEEY of the nanostructure becomes weak at relatively high primary electron energy. To verify the simulation results, we fabricate several silver nanostructures by thermal evaporation with gas pressure varied from 40 to 70 Pa. Measurement results indicate that all the fabricated nanostructures can suppress TEEY to some degree; and the more top hemispherical nanograins the nanostructure possesses, the higher TEEY revealed. For the measured SEE characteristics of the nanostructures fabricated at 40 and 45 Pa, we observe a higher BSEY than that of the flat surface. These experimental results qualitatively verify the simulated estimations. This work is of significance to comprehend SEE characteristics in related applications such as multipactor suppression.

Secondary electron (SE) emission (SEE) from material surfaces is a frequent phenomenon in space and vacuum environments. SEE modulation is important since it governs the performance of some devices such as electronic multipliers or induces some detrimental effects such as multipactors. Surface coating has been reported to modulate SEE effectively, whereas SEE behaviors of coating structures are not clearly understood yet, and the appropriate theory to describe SEE characteristics quantitatively for coating structures is less developed so far. Here, we have prepared four alumina coatings possessing various thicknesses to research the SEE characteristics of coating structures and have shown how the coating thickness affects the SEE behaviors. Besides, by considering coating/substrate as an ideal double-layer structure, we have derived several equations to describe the producing, transmitting, and escaping processes of excited inner SEs and finally constructed a unidimensional SEE model for double-layer structures. The model is applicable to reveal the dependence of true SE yield (TSEY) on the top and bottom layers’ physical properties and estimate TSEY proportions contributed by the top and bottom layers at random energy points. By employing the concept, SEE characteristics of Al₂O₃/Si, MgO/Si, and TiO₂/Si double-layer structures have been quantitatively interpreted. Moreover, the abnormal SEY curve with a double-hump shape, which is induced by the peak position distinction of SiO₂/Si structures, can also be explained. This work is of great significance to comprehend TSEY modulating regularities of various double-layer structures applied in surface engineering.

We study secondary electron yield (SEY) suppression of silver using a hyperbranched nanostructure obtained by thermal evaporation. First, we perform thermal evaporation at different residual gas pressures for studying the influence of pressure on surface morphologies. A self-assembled hyperbranched Ag nanostructure has been achieved at 100 Pa. Then, we further investigate the detailed formation process of the self-assembled hyperbranched Ag nanostructure qualitatively and find it to be dominated by “screening effect”. Finally, we study the obvious SEY suppression effect of this special structure. We show that 100 Pa is the best process condition within our experimental scope from the SEY suppression point of view. It exhibits maximum SEY (δ_max) of ∼0.9. We also show that the combining of this nanostructure with the micro-porous surface we developed before can further improve its SEY suppression effect which leading to a δ_max of ∼0.8. We propose a novel 2D rectangular-hemisphere hybrid trap model to perform numerical simulation of secondary electron dynamics for interpretation of the experimental results. In total, this work provides guidance to controllable preparation of low SEY metallic surfaces for potential applications in particle accelerators, RF microwave components and satellite systems.

One problem with current 3D printed microwave components is that they usually have more surface roughness than components manufactured with traditional machining processes. To estimate the multipactor threshold of 3D printed microwave components, it is important to evaluate the total secondary electron yield (TSEY) of the random rough surface. In this work, taking copper as an example, we conduct TSEY simulations for random rough surfaces. First, we generate both isotropic and anisotropic Gaussian type random rough surfaces; then, the dependence of the TSEY on both the roughness and correlation length is studied using Monte-Carlo simulations. Results show that when the root-mean-square roughness increases from 0 to 30 μm, the maximum TSEY increases slowly at first and then decreases rapidly. In other words, roughness can also enhance and not just suppress the TSEY. The results can be interpreted as follows: for a relatively smooth/rough surface, the TSEY enhancement/suppression induced by oblique incidence/a shadowing effect plays a dominant role. Simulation results also show that correlation length has a notable effect on the TSEY. Furthermore, for anisotropic surfaces, the azimuthal angle also influences the TSEY. Compared with currently published work, we provide an optional evaluation method for the TSEY of random rough surfaces. The predictions in this work not only confirm existing observations (the TSEY suppression effect) but also present new predictions (the TSEY enhancement effect and the azimuthal angle effect).

With the development of space technology, microwave components with increased power handling capability and reduced weight have been urgently required. In this work, the perforated waveguide technology is proposed to suppress the multipactor effect of high power microwave components. Meanwhile, this novel method has the advantage of reducing components' weight, which makes it to have great potential in space applications. The perforated part of the waveguide components can be seen as an electron absorber (namely, its total electron emission yield is zero) since most of the electrons impacting on this part will go out of the components. Based on thoroughly benchmarked numerical simulation procedures, we simulated an S band and an X band waveguide transformer to conceptually verify this idea. Both electron dynamic simulations and electrical loss simulations demonstrate that the perforation technology can improve the multipactor threshold at least ∼8 dB while maintaining the acceptable insertion loss level compared with its un-perforated components. We also found that the component with larger minimum gap is easier to achieve multipactor suppression. This effect is interpreted by a parallel plate waveguide model. What's more, to improve the multipactor threshold of the X band waveguide transformer with a minimum gap of ∼0.1 mm, we proposed a perforation structure with the slope edge and explained its mechanism. Future study will focus on further optimization of the perforation structure, size, and distribution to maximize the comprehensive performances of microwave components.